WO0200652 discloses compound I ((R)-3-fluorophenyl-3,4,5-trifluorobenzylcarbamic acid 1-azabicyclo[2.2.2]oct-3-yl ester) which has the following formula (I)

Compound I is also disclosed in WO2004000840. On the other hand, compound I is exemplified as hydrochloride salt in WO2003053966 as an intermediate in the synthesis of other compounds. However, this acid addition salt known from the prior art had the disadvantage that its physicochemical stability was poor. Upon storage or formulation of said known salt, progressive decomposition and concomitantly an increase in the amount and number of impurities was observed. Obviously, this problem is further aggravated under demanding environmental conditions such as light, heat, humidity or acidity.